This invention relates generally to a semiconductor sealing mold and a method of encapsulating a semiconductor element employing a semiconductor sealing mold and more particularly to a semiconductor sealing mold employed in a method of encapsulating a semiconductor element via a resin sealing process.
FIG. 2A is a plane view of a lead frame connected semiconductor element, and FIG. 2B is a sectional view along the line 2B--2B in FIG. 2A disclosing a semiconductor sealing mold 20 as known in the art. Semiconductor element 8 is secured to lead frame 1 via semiconductor element mount 6, such as, with an adhesive or eutectic alloy. The output pads of semiconductor element 8 and internal leads 2 of lead frame 1 are connected by a plurality of bonding wires 16 comprising fine metal wire, such as, gold or copper-aluminum. Further, a dam bar 3 is formed between internal leads 2 and external leads 4 of lead frame 1. Also, pilot holes 5 and outer frame 7 may be formed external of lead frame 1.
Previously employed semiconductor sealing molds have resin inflow openings 10 formed in a lower mold portion 14 so that they are only in communication with the side wall regions of lower mold cavity 12B. Semiconductor apparatus employed in connection with such semiconductor sealing molds require initial alignment of lead frame 1 between upper mold portion 13 and lower mold portion 14 of the semiconductor sealing mold, followed by heating these mold portions at a temperature between 160.degree. C. to 180.degree. C., and thereafter compressing lead frame 1 between mold portions 13 and 14 at a predetermined pressure. Then, a thermosetting resin having a low viscosity is introduced at resin inflow opening 10 and runner 11 to the interior of the compressed and heated mold portions 13 and 14 to bring about filling of the mold cavity 12. However, since resin inflow opening 10 is provided within the confines of lower mold portion 14 relative to lead frame 1, the thermosetting resin flowing into cavity 12 from resin inflow opening 10 is actually blocked by the presence of lead frame 11 so that lower mold cavity 12B will fill at a faster rate than upper mold cavity portion 12A. In other words, in the encapsulation of semiconductor element 8, the flow of resin in the mold cavity was directed towards semiconductor element from one direction only. In this manner, the resin forced into cavity 12 flows from lower mold cavity 12B into upper mold cavity 12A and, as a result, the force of the resin flow through and about lead frame 1 will shift semiconductor element mount 6 and internal leads 2 toward the upper reaches of upper mold cavity 12A. This approach in mold filling tends to damage semiconductor element 8 and/or its leads. For example, (1) The position of the semiconductor element 8 relative to lead frame 1 is deformed, disarranged or twisted. (2) Internal leads 2 of lead frame 1 are deformed. (3) Adjacently disposed bonded wires are brought into contact causing electrical shorts or the bonded wires are severed or broken. All of these problems result in significant deterioration or destruction of the useful life of the lead frame connected semiconductor element.
The present invention resolves these problems and has as an object of providing a semiconductor sealing mold that avoids or eliminates the foregoing problems.
It is another object of this invention is to provide a semiconductor method of encapsulation of a semiconductor element in resin that presents damage to the semiconductor connections to its lead frame during the sealing or encapsulation process.
It is a further object of this invention to provide means to increase the yield of lead frame connected semiconductor elements subjected to a semiconductor sealing mold process wherein they are encapsulated in a resin material.
It is another object of this invention to provide a semiconductor sealing mold to prevent the occurrence of fundamentally fatal defects in the employment of semiconductor sealing apparatus, such as, a distorted position change of the semiconductor element relative to its lead frame or mount, deformation of the lead frame internal leads, and undesirable electrical contact between adjoining bonding wires or the severing of bonding wires.